Iron-nickel-silicon alloys



United States Patent Ofice Patented July 18, 1961 2,992,917 IRON-NICKEL-SILICON ALLOYS Roger A. Perkins, Tonawanda, and Claude R. Bishop,

Niagara Falls, N.Y., assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 29, 1958, Ser. No. 783,184

12 Claims. (Cl. 75-423) V This invention relates to an iron-nickel-silicon alloy and, more particularly, to an acid resistant iron-nickelsilicon alloy amenable to hot-working.

The addition of silicon to an iron and/or nickel base alloy is known to produce alloys having excellent resistance to acid. However, the concentration of silicon required to promote acid resistance is such that the alloys are generally unworkable and, therefore, are suited only for use in the cast condition. Attempts to achieve ductility by lowering the silicon content of the alloys have been successful only at a sacrifice in corrosion resistance of the alloys. Nevertheless, the demand continues for a high silicon alloy which combines good resistance to the corrosive eifects of acids, such as sulfuric acid, and which can be formed into a variety of sheet, bar, and other wrought products.

Accordingly, it is an object of this invention to provide a corrosion-resistant high silicon alloy which can be readily hot-worked.

Another object of this invention is to provide an improved process for the production of a corrosion-re sistant, hot-workable, formable high silicon alloy.

Other objects and advantages of this invention will be apparent from the following description and appended claims.

The objects of this invention are accomplished by providing an alloy consisting essentially of 28 to 60 weight percent nickel, 9 to 12.2 weight percent silicon, and the balance iron and incidental impurities.

In order to obtain the acid-resistant, hot-workable properties of the alloy of this invention, the nickel content must be between about 28 to 60 weight percent, the silicon content between about 9.0 and 12.2 weight percent, with the silicon content preferably being in excess of about 10 weight percent, and the balance iron and incidental impurities. In the preferred form of this invention, the nickel content is between about 30 and 50 weight percent, the silicon content between about 10.2 and 12.0 weight percent, and the balance iron and incidental impurities.

Several iron-nickel-silicon alloy compositions that satisfy the compositional ranges for this invention, as set forth above, and other iron-nickel-silicon alloy compositions falling Without these ranges were prepared by induction-melting the constituents of the alloy in a magnesia crucible in air. These alloy compositions were compared to demonstrate the hot-working characteristics of the alloy of this invention. The results of these tests are as set forth in Table I below:

TABLE I Workabzlzty of the alloy of this invention at 1050 C.

Ni Fe Forge- Roll- Extrudabllity ability ability 9.4 25 Balance-.- Poor 9.4 30 do Good 8.5 35 do POOL--- 10.0 35 do Good-.. 8.6 40 .--do Peon.-- 10.0 40 do Good 10.5 25 9.4 30 8.5 35 9.5 35 11.5 35 8.6 40 10.4 50 9.6 35 10.7 35 11.6 35 12.8 35

The alloy compositions designated as good were free from cracks after hot-working, while those designated as poor were cracked and in many instances were in pieces.

To determine the corrosion-resistance of the alloy of this invention, several of the iron-nickel-silicon alloy compositions from Table I were tested in boiling sulfuric acid. The results of these tests are set forth in Table 11 below:

TABLE II Corrosion resistance of the alloy of this invention Inch penetration per month Ni Condition The results of the tests in Tables I and II show that the iron-nickel-silicon alloy of this invention possesses good workabilty, whether rolled, forged, or extruded, and excellent resistance to boiling sulfuric acid. It has been found that the alloy of this invention can be hot-worked only in a narrow temperature range near the melting point- The temperature ranges from about 900 C. to about 1075 C. and preferably at about 1050 C. As the silicon content of the alloy is increased, the hot-working temperature range decreases proportionately up to a temperature of between about 1000 C. and 1050 C., which is the optimum temperature range for hot-working the alloy of this invention. Hot-working the alloy at temperatures below about 900 C. promotes cold-shortness while hot-working the alloy at temperatures above about 1075 C. promotes hot-shortness.

EXAMPLE I An alloy consisting of 11.6 percent silicon, 35 percent nickel, and the balance iron and incidental impurities was prepared by induction-melting silicon metal, electrolytic nickel, and technical grade iron in a magnesia crucible in air. The melt was cast as a 3-inch diameter extrusion billet and cooled to room temperature. The alloy so produced was heated to 1050" C. and reduced by high-speed extrusion in one pass to a l A-inch diameter bar. The alloy extruded without difliculty and a sound bar with a good surface was obtained. This alloy was tested for corrosion resistance in boiling 55 percent H 80 and 77 percent H 80 respectively. In boiling 55 percent H 80 the inch penetration per month was 0.00046; and in boiling 77 percent H 80 the inch penetration per month was 0.00084.

EXAMPLE II An alloy composed of 10 percent silicon, 35 percent nickel, and the balance iron and incidental impurities was prepared in the manner set forth in Example I. This melt was cast into a 2 inch by 2 inch square castiron ingot mold, cooled to room temperature, and heated in a gas-fired furnace to 1050 C. A portion of this alloy was rolled into an 0.25-inch thick plate 2.5 inches wide and another portion into an 0.04-inch thick sheet. The plate was tested for strength and ductility by a beam load test over 12-inch centers. The plate sustained a 1500-pound load with a maximum deflection of 1.14 inches before failure. These results indicate good mechanical strength and ductility for an alloy of this type.

EXAMPLE III An alloy composed of 9.3 percent silicon, 30 percent nickel, and the balance iron and incidental impurities was prepared in the manner set forth in Example I. This melt was cast into a 2-inch by 2-inch square ingot mold, cooled to room temperature, heated to 1050 C., and hammer-forged to a %-inch square bar. The bar was groove-rolled at 1=050 C. to a /z'inch diameter rod. Portions of the bar were given a homogenization anneal at 1100 C., followed by air cooling. Standard ASTM 0.25'-inch diameter tensile specimens were prepared and tested at room temperature. The alloy had the following properties:

Yield strength (determined at 0.2 percent offset) ..p.s.i. 78,300 Ultimate strength p.s.i. 130,000 Elongation in 1 inch percent 2 Reduction of area percent v 3 These properties are excellent for high silicon acid-resistant alloys.

What is claimed is:

1. An acid-resistant alloy characterized by substantiallycrank-free hot-workability in the temperature range of from about 900 C. to 1075 C. and consistingessentially of 28 to 60 weight percent nickel, 9 to 12.2 weight percent silicon, andthe balance iron and incidental. impurities.

2. An alloy in. accordance with claim- 1, wherein the silicon content is at least about 10.2 weight percent and at a maximum of 12.2 weight percent.

3. An acid-resistant alloy characterized by substantially crack-free hot-workability in the temperature range of'from about 900 C. to 1075 C. and consisting essentially of 30 to 50 weight percent nickel, 10.2 to 12.0 weight percent silicon, and the balance iron and incidental, impurities.

4. An acid-resistant alloy characterized by substantially crack-free hot-workability in the temperature range of from about 900 C. to 1075 C. and consisting of about 35 weight percent nickel, about 10.5 weight percent silicon, and the balance iron and incidental impurities.

5. Hot-worked, acid-resistant forgings, extrusions, rods, sheets, plates, and like products, which products are substantially free from cracks induced by hot-working and consist essentially of 28 to 60 weight percent nickel, 9 to 12.2 weight percent silicon, and the balance iron and incidental impurities.

6. Hot-worked, acid-resistant products in accordance with claim 5, wherein the silicon content is at least about 10.2 weight percent and at a maximum of 12.2 weight percent.

7. Hotworked, acid-resistant forgings, extrusions, rods, sheets, plates, and like products, which products are substantially free from cracks induced by hot-working and consist essentially of 30 to 50 weight percent nickel, 10.2 to 12.0 weight percent silicon, and the balance iron with incidental impurities.

8. Hot-worked, acid-resistant forgings, extrusions, rods, sheets, plates, and like products, which products are substantially free from cranks induced by hot-Working and consist of about 35 weight percent nickel, about 10.5 weight percent silicon, and the balance iron and incidental impurities.

9'. A process for the production of acid-resistant articles which comprises melting and casting a mixture of iron, nickel, and silicon to produce an ingot consisting of 28 to 60 weight percent nickel, 9 to 12.2 weight percent silicon, and the balance iron and incidental impurities; heating said ingot to a temperature in the range of from about 900 C. to about 1075 C.; hot-working said heated ingot at a temptrature in said range to form a shaped article; and cooling said shaped article.

10. A process in accordance with claim 9, wherein said ingot is hot-worked at a temperature of about 1050. C.

11. A process for the production of acid-resistant articles which comprises melting and casting a mixture of iron, nickel, and silicon to produce an ingot consisting of 30 to 50 weight percent nickel, 10.2 to 12.0 weight percent silicon, and the balance iron and incidental impurities; subsequently heating said ingot to a temperature in the range of from about 900 C. and 1075 0.; hotworking said heated ingot at a temperature in said range to form a shaped article; and cooling said shaped article.

12. A process for the production of acid-resistant articles which comprises melting and casting a mixture of iron, nickel, and silicon to produce an ingot consisting of about 35 weight percent nickel, about 10.5 weight percent silicon, and the balance iron and incidental impurities; subsequently heating said ingot to a temperature in the range of from about 900 C. and 1075 0.; hotworking. said heated ingot at a temeprature in said range to form. a shaped article; and cooling said shaped article.

References Cited in the file of this patent UNITED STATES PATENTS 1,556,776 Flintermann Oct. 13, 1925 1,759,477 Armstrong May 20, 1930 OTHER REFERENCES Metals Handbook, 1948 edition, pages 1217, 1233 and 1266, published by the American Society for Metals, Cleveland, Ohio.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION.

Patent No, 2,992,917 July 18, 1961 Roger A. Perkins et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent. should read as corrected below.

Column 3, line 55, for "crank-free" read crack-free column 4, line 25, for "cranks" read cracks Signed and sealed this 5th day of December 1961.

(SEAL) Attest: I

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents} USCOMM-DC- 

1. AN ACID-RESISTANT ALLOY CHARACTERIZED BY SUBSTANTIALLY CRANK-FREE HOT-WORKABILITY IN THE TEMPERATURE RANGE OF FROM ABOUT 900*C. TO 1075*C. AND CONSISTING ESSENTIALLY OF 28 TO 60 WEIGHT PERCENT NICKEL, 9 TO 12.2 WEIGHT PERCENT SILICON, AND THE BALANCE IRON AND INCIDENTAL IMPURITIES. 